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Journal of Experimental Biology, Vol 200, Issue 4 713-721, Copyright © 1997 by Company of Biologists
JOURNAL ARTICLES |
Y Naitoh, T Tominaga, M Ishida, A Fok, M Aihara and R Allen
To examine the forces needed for discharge of the fluid contents from the contractile vacuole of Paramecium multimicronucleatum, the time course of the decrease in vacuole diameter during systole (the fluid-discharging period) was compared with that of various vacuole discharge models. The observed time course did not fit that predicted by a model in which contraction of an actin­myosin network surrounding the vacuole caused discharge nor that predicted by a model in which the surface tension of the lipid bilayer of the vacuole caused discharge. Rather, it fitted that predicted by a model in which the cell's cytosolic pressure was responsible for discharge. Cytochalasin B, an effective inhibitor of actin polymerization, had no effect on the in vivo time course of systole. An injection of a monoclonal antibody raised against the proton pumps of the decorated spongiomes (now known to be the locus of fluid segregation in P. multimicronucleatum) disrupted the decorated spongiomes and reduced the rate of fluid segregation, whereas it did not alter the time course of systole. We conclude that in P. multimicronucleatum the internal pressure of the contractile vacuole is caused predominantly by the cytosolic pressure and that the fluid-segregation mechanism does not directly affect the fluid-discharge mechanism. Elimination of this cytosolic pressure by rupturing the cell revealed the presence of a novel fluid-discharge mechanism, apparently centered in the vacuole membrane. The involvement of tubulation of the vacuole membrane as the force-generating mechanism for fluid discharge in disrupted cells is discussed.
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  E.-M. Ladenburger, I. Korn, N. Kasielke, T. Wassmer, and H. Plattner An Ins(1,4,5)P3 receptor in Paramecium is associated with the osmoregulatory system J. Cell Sci., September 1, 2006; 119(17): 3705 - 3717. [Abstract] [Full Text] [PDF]
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 K. Sugino, T. Tominaga, R. D. Allen, and Y. Naitoh Electrical properties and fusion dynamics of in vitro membrane vesicles derived from separate parts of the contractile vacuole complex of Paramecium multimicronucleatum J. Exp. Biol., October 15, 2005; 208(20): 3957 - 3969. [Abstract] [Full Text] [PDF]
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M. Iwamoto, K. Sugino, R. D. Allen, and Y. Naitoh Cell volume control in Paramecium: factors that activate the control mechanisms J. Exp. Biol., February 1, 2005; 208(3): 523 - 537. [Abstract] [Full Text] [PDF]
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M. Iwamoto, R. D. Allen, and Y. Naitoh Hypo-osmotic or Ca2+-rich external conditions trigger extra contractile vacuole complex generation in Paramecium multimicronucleatum J. Exp. Biol., December 15, 2003; 206(24): 4467 - 4473. [Abstract] [Full Text] [PDF]
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C Stock, R. Allen, and Y Naitoh How external osmolarity affects the activity of the contractile vacuole complex, the cytosolic osmolarity and the water permeability of the plasma membrane in Paramecium multimicronucleatum J. Exp. Biol., January 1, 2001; 204(2): 291 - 304. [Abstract] [PDF]
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T Tominaga, Y Naitoh, and R. Allen A key function of non-planar membranes and their associated microtubular ribbons in contractile vacuole membrane dynamics is revealed by electrophysiologically controlled fixation of Paramecium J. Cell Sci., January 11, 1999; 112(21): 3733 - 3745. [Abstract] [PDF]
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